Abstract

Sensors based on surface plasmons or waveguide modes are at the focus of interest for applications in biological or environmental chemistry. Waveguide-mode spectra of 1 μm-thick pure and perforated silica films comprising isolated nanometric holes with great aspect ratio were measured before and after adhesion of streptavidin at concentrations of 500 nM. The shift of the angular position for guided modes was nine times higher in perforated films than in bulk films. Capturing of streptavidin in the nanoholes is at the origin of that largely enhanced shift in the angular position as the amplitude of the guided mode in the waveguide perfectly overlaps with the perturbation caused by the molecules. Hence, the device allows for strongly confined modes and their strong perturbation to enable ultra-sensitive sensor applications.

Figures (7)

(a). Calculated reflectivity as a function of the angle of incidence and the polarization for a typical sample as employed in the present investigations. Dips in the reflectivity are associated to be guided modes in the waveguide or to surface plasmon. (b). Amplitudes of excited guided modes. Glass prism, gold film, silica glass and water are lined from left to right. Each boundary is presented by a green line. Scale bars of the field strengths were shown on each right hand side.

Schematic of the supermolecule architecture of a silica film in preparation for streptavidin capture. A hydrophilic surface of a silica film was obtained in alkali solution. 3-aminoprophyltriethoxysilane (3APT) was used as the silane coupling agent. The 3APT-modified substrate was immersed in 0.5 mM 5-[5-(N-succinimidyloxycarbonyl) pentylamido]hexyl D-biotinamide (biotin-(AC5)2-OSu) solution in 1/5 M PBS buffer for amide coupling with the 3APT layer.

(a). TE0 mode of the waveguide before (black) and after (red) modification with 500-μM biotin. Shift of the dip position was less than 0.01°. (b). TE0 mode of the silica waveguide substrate with a density of 1 ×1010 cm-2 holes before and after modification with 500-μM biotin.